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Discussion Starter · #1 ·
I'm thinking of maybe changing from carb to Holley or Fitech EFI.

I know that changing from dual to single plane intake reduce the bottom end hp and increase top end hp.
Does this happen in the same amount, if I change to EFI at he same time?
Or is the EFI system able to keep the low end power better that what the carb would have done?
Engine is a 380 hp Chevy Small block with Vortec heads.
Intake is an Edelbrock RPM AirGap Dual plane.
Car is a 34 Ford Roadster. Manual trans.
 

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My understanding is that the dual plane provides a more consistent vacuum signal to the carburetor across the rpm range, which improves driveability and low end power. However, since EFI does not rely as much on the consistent vacuum signal, and can be tuned more easily to compensate, the single plane manifold should usually work fine. If you choose port injection EFI it is even less dependent on vacuum signal to get a consistent mixture.

If I decide to try throttle body EFI I may just experiment with removing the 4 hole carburetor spacer from my dual plane and using an open spacer instead. I need the spacer to let the air cleaner clear tall valve covers, and I don’t have any hood clearance issues.

I’ve also been looking closely at the Edelbrock Pro-Flo 4 port EFI and trying to decide if it’s a good choice. It includes the port injection intake and distributor. It also has a distributor and timing controls, and it should all be designed to work together. It’s not really that much more expensive than other systems (about $1,900) if you consider the parts they include .
 

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Well your dual plane already has the notch and that sometimes hurts low end. Plus I'll assume your 34 roadster is light-ish and being a manual that is also more friendly to a single plane since your the stall basically. Not to mention vortec heads have good low/mid drive-ability. Just depends on your cam, headers length and rear gear but you got a lot of the factors that should offset the low end loss of a single plane. I'd prob try a smaller one like the Holley 300-261, think it was orig a multi-port intake anyway. Been wanting to try one of those myself.
 

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I can not give a lot of information on the intake swap deal when going to TBI setup like the aftermarket units that are available, but I have read on some folks who went from going from a carburetor on a dual plane high rise intake and then swapping out to a TBI unit that with the dual plane intake they had some fuel distribution issues and some slight tuning headaches and had some areas of driving that problems would arise that they could not get things tuned out well and the self adjusting system seemed to struggle.

Now I don't know the specs of the build as timing and also camshaft specs and compression and vacuum signal and man other factors will play into things a lot more. They ended up swapping out the dual plane intake and went with an open intake manifold and the swap helped out quite a bit and the problem areas that they had trouble with for the TBI unit to work was all fixed and they now had no more tuning and running issues across the board.

I read something about the unit having a hard time getting an accurate reading because of the intake manifold on the dual plane being cutoff between the two sides vs the open intake which give the TBI unit to have access to get readings from all 8 cylinders which allows for a better more precise reading of what is going on between things.

Also something also with the dual plane intake being higher and then lower from side to side played into things as well. I read it has something to do with the MAP sensor being on the one side of the throttle body unit and without it being able to read the other side of the engine it would not see all the signals from all cylinders.

Holley recommends going from a dual plane intake to a single plane intake if changing from a carb setup to a TBI setup on there sniper systems. I have also read some folks had no issues with sticking with a dual plane intake and if they did have issues with a dual plane intake they went with an open spacer or if they had an edelbrock rpm air gap intake with the notched plenum then they did not have problems.

Sorry I can't help more as I have only read a few things about doing the setup change. It might differ between the different throttle body fuel injection units being used and there design.

You might want to do a lot of research on the topic in order to save yourself some potential problems. Take some of my stuff as a grain of salt though as results vary quite a bit across the board. I have done some research on the swapping out just looking at things in case I would ever go that route myself in the future.
 

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I have a G7 BBC that I plan to run a dual plane with MP injection, I will likely cut out the plenum divider and mill vertical slots so I can put in varying height dividers as reqd.
 

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The whole single vs dual plane deal is about the tuning and length of the intake runners and fitting it into a package that fits under low hoods... the length and diameter of the runners determines the ramcharging tuning effect of the intake tract air charges... the dual plane's runners are long enough to provide some ramcharging of the air into the cylinders at mid RPMs say 1500 - 4500 RPMs and a torque boost which is desirable for accelerating heavy vehicles and economical cruising... the low rise single plane's runners tend to be too short to do that, just allow lots of airflow at high RPMs for more HP... At first glance, the runners on a single and dual plane intakes look to be about the same length but closer inspection of dual planes shows runners for left side of engine get air at right side of intake... and vice versa... via the divided plenum... yielding longer runners...
Cross ram intakes, long runner ram intakes, tunnel rams, TPI, torque tube carb.s/EFI (i.e. Webers/Hilborn), and EFI 'barrel' intakes do similar things while not necessarily feeling restricted to fitting under low hoods...
The first EFI V8's in the '75 Cadillac Seville used an aluminum low rise, well flat, single plane intake with direct port injection/8 injectors on an Olds 350" engine... later the engine designers sought to get back some of the early EFI's missing mid RPMs torque and cruising MPG with more elaborate intake manifold designs such as Tuned Port Injection/TPI...
The dual plane/EFI problem Eric mentions is with TBI/Throttle Body Injection and wet air intake flow like when using a carb... with 8 direct port injectors the intake has dry air flow...
In this video, they were hoping the dual quad tunnel ram intake manifold, a type of single plane, they were using had long enough intake runners to preserve 'dual plane' mid RPMs torque:
Mid RPMs Torque?
 

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As has been noted, longer, smaller runners tend to favor low RPM torque but can run out of breath up high. Short, fat runners like a single plane might have don't have quite the velocity of air down low to make the best use of inertia of the air flow.

In EFI, it's less of an issue, but still present. One of the things you need to try to imagine is how different the airflow is depending on where the fuel is introduced. If it's port EFI, the air in the intake is just air and therefore has far less mass than an intake with a carb or TBI, so the intake design matters less with port EFI.

With a carb, the intake choice matters a lot for three main reasons: 1- how it delivers vacuum to the carb, or what the carb "sees" from the vacuum in the plenum, 2- the quality of the air flow and how it keeps the fuel suspended, and 3- how the mass of fuel/air behaves in the runner is always a trade-off of bulk flow vs velocity/inertia.

With TBI, you basically eliminate #1 because it's an active fuel injection instead of a passive mechanism. You still have to deal with #3, and you still have a small impact from #2.

Port EFI eliminates #1, eliminates #2, and #3 is less of an issue because the air in the runners isn't carrying the additional mass of fuel.

A good example is an LT1. Super short runners, but it's a low RPM torquey motor. Because of the port EFI, the intake design was chosen for packaging and it doesn't seem to affect its ability to function in the desired RPM range.
 

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Actually, the LT1 was missing mid RPMs torque but over came that somewhat by simply making more HP than the previous TPI torque biased engines. Then the LSx engines intakes attempted to make a better balance of torque vs HP.
Long ago, back when Richard Holdener still had hair, he did what is the definitive dyno testing article on EFI vs intake designs:
EFI Intakes
 

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Depend on whether you’re considering aftermarket TBI versus a factory style TBI or Port Injection.

Aftermarket TBI and all Port Injection systems work better on an open plenum, single plane style intake. For aftermarket TBI a dual plane with either an open spacer or the divider milled down about 5/8’s to 3/4’s inch acts much the same as an single plane while retaining quite a lot of the dual plane lower end torque advantages.

The low pressure original factory and old Holley TBI’s really don’t care they act in relation to the intake type more as carburetors do to whit what you’ll see is higher and flatter torque curve with a lower power peak but still carrying over some RPM’s on a dual plane. Where these on a single plane drop some bottom and mid torque but return with a top end rush out at peak power where both the torque and power maximums tend to be peaky.

Certainly the cam and compression have a lot to do with this as does engine displacement. Long duration cams say getting oh-fifty over 220 degrees and LSA’s under 110 degrees tend to trade lower and mid range torque for top end horsepower. Higher compression maintains or restores bottom through mid RPM torque and carries top end horsepower to higher maximum and flatter over a longer rev range. Lots of cubic inches generate lots of torque which hides most low to mid RPM torque loses where smaller engines suffer these more noticeably.

Piston crown design enters into this as well where flat top and D dish pistons compared to round dish factory style pistons produce better torque and power values throughout the rev range. This also gets into squish/quench clearance and area. Tighter squish quench begets better performance from torque and power to fuel economy and lower emissions. Flat tops an D dish pistons also put more surface area under the squish step which increases the area to volume ratio on this side of the chamber thus sinking more excess end burn heat that leads to detonation. Generally for street cruisers and street performance engines the best results are .035 to .040 inch clearance. For extreme performance this may be reduced to as much as zero clearance where the rewards of winning offset the costs of occasional engine failure from piston to head collisions.

Bogie
 

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Don't expect the change from carb. to EFI to really net you much of anything over a properly tuned and sized carb... the auto manufacturers did it mainly to meet emissions requirements...
V V T/Variable Valve Timing, variable intake tract length, cylinder deactivation, and D.I./Direct Injection which injects super high pressure gasoline directly into the combustion chamber similar to diesel engines give a jump in performance over carb.s/EFI, but they're not a home build thing...
You might consider adding 8 injectors to the Performer RPM AirGap intake... plus an EFI controller computer/ECM, throttle body, and pump... if have money to burn...
 

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Discussion Starter · #11 ·
Thanks for your inputs.
It's just a thought, so far.
Motor it's a '93 Chevy small block 1st gen flat top piston stock factory roller block with reworked vortec heads ,015 shim gaskets, app 9,8:1 compression roller rockers and a Howards cam 183215-14.
No space issues under the hood.
I do have a 4 hole 1/2 inch spacer that could be changed to an open one, tow.
618327
 

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Depending on compression height (C.H.) of pistons, number/style of valve reliefs, rocker arm ratio, size of carb., and if headers, I'd estimate your well designed/well built engine at up to 10.4 - 10.5:1 compression ratio and 420 - 440 HP @ 5800 - 6000 RPMs...
 
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